What is the theme in Albion's Seed: Four British Folkways in America by David Hackett Fischer?

The main theme would be British colonial culture. The British, led by the English, extended themselves to spend a few centuries as a great Empire of the modern age. They were able to do this thanks in part to all of their cultural and technological advances, some of which were a precious inheritance, well worked over for a millennium, of Roman empirical knowledge.